As you can see, rarities are found in two major pulses, each corresponding with migration, not surprisingly. The slowest time of the year is the dead of winter, roughly mid January until mid-March. The second slowest period is from mid-June until the end of July. The last two weeks of June are particularly sparse. Here is the complete list of every OBRC-reviewable rarity, found being the dates of June 18 and June 30 in Ontario (current to June, 2011). Hopefully I did not miss any!
Eurasian Collared Dove - June 24, 1998, Burlington (found by John Keenleyside)
White Ibis - June 27, 1998, Pelee Island (found by Ethan Meleg, David Hodare)
Western Grebe - June 20, 1999, Rainy River (found by David Elder, Karen Mikolieu)
White-winged Dove - June 27 to July 1, 2001, Thunder Bay (found by David and Ann Christianson)
White-winged Dove - June 30, 2002, west of Kingsville (found by Stu Mackenzie)
Northern Wheatear - June 23, 2003, Point Petre (found by Robert Maurer Jr.)
Scissor-tailed Flycatcher - June 26, 2004, St. Clair NWA (found by Cecilia Verkley)
Henslow's Sparrow - June 19 to July 7, 2005, southern Chatham-Kent (found by Alan Wormington, Keith Burk, E. Jane Burk)
|keep checking those nice fields for Henslow's....|
McCown's Longspur - June 21, 2005, Weagamow Lake, Kenora District (found by Pete Read, Josh Shook). This is the only record for Ontario.
Prairie Warbler - June 20, 2006, Thunder Cape (found by John Woodcock)
California Gull - June 29, 2006, Point Pelee (found by Alan Wormington)
Black Vulture - June 22, 2008, Tobermory (found by Tom Thomas and Tim King)
Brown Pelican - June 27, 2009, Point Edward (found by Daniel and Sara Miller)
Barn Owl - June 30, 2009, Blenheim (found by Brandon Holden and Ken Burrell)
Chuck-will's-widow - June 18 to July 28, 2010, Kirkfield (found by Martin Parker et al.)
Scissor-tailed Flycatcher - June 19, 2010, Kenora District (found by Lillian Anderson)
As you can see, there are not a lot of megas on this list, apart from the provincial first record of McCown's Longspur way in the north. The White Ibis was a good one too!
Other common themes for the time of year include rare breeding birds (Barn Owl, Western Grebe, Henslow's Sparrow, Chuck-will's-widow (it was on territory for the summer!)) and rare doves.
If anyone is so inclined to look for rarities this time of year, that list may give you an idea of the possibilities, if past trends have any bearing on the future! Personally, I know I'll be spending my summer doing other things...
I thought I would post the link the the photos of the TUFTED PUFFIN that Ralph Eldridge found on Machias Seal Island in New Brunswick on June 17 (which is still present, but very elusive). This is the first east coast record since one in Maine in the 1830s. What a crazy bird!! Tufted Puffins are a Pacific species, though there are two recent records from Europe. Perhaps with all the melting sea ice the odd one is finding its way through the Northwest Passage! It is one of those "dream birds" that I'm always keeping an eye out for at Netitishi Point...